This application relates to a gas turbine engine wherein cooling air passes through a boost compressor to be delivered to a turbine section for cooling.
Gas turbine engines are known and typically include a fan delivering air into a bypass duct as propulsion air and into a compressor as core air. The air is compressed in the compressor and delivered into a combustor where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate. The turbine rotors, in turn, drive the compressor and fan rotor.
As known, the turbine components see very high temperatures. As such, it is known to deliver cooling air to the turbine.
Historically, the fan rotor rotated as one with a fan drive turbine. However, more recently, a gear reduction is placed between the fan rotor and the fan drive turbine. With this change, the fan may rotate at slower speeds than the fan drive turbine. This allows a designer to increase the speed of the fan drive turbine. This increase results in higher temperatures in the turbine section.
The higher temperatures raise cooling challenges. The higher temperatures also results in higher pressures at an upstream end of the turbine section. This is where one branch of the cooling air is typically delivered. As such, the cooling air must be at a sufficiently high pressure that it can move into this environment.
Historically, air from near a downstream end of the compressor section has been tapped to provide cooling air. However, with the move to a geared gas turbine engine, the efficient use of all air delivered into the core engine becomes more important. As such, utilizing air which has already been fully compressed is undesirable.
Recently, it has been proposed to tap the cooling air from a location upstream of the downstream most location in the compressor. This air is then passed through a boost compressor, which increases its pressure such that it now can move into the turbine section.